The local supermarket buys lettuce each day to ensure fresh produce. Each morning any lettuce that is left from the previous day is sold to a dealer that resells to farmers who use it to feed the animals. This week the supermarket can buy fresh lettuce for $4 a box. The lettuce is sold for $10 a box and the dealer that sells old lettuce is willing to pay $1.50 a box. Past history says that tomorrows demand for lettuce averages 250 boxes with a standard deviation of 34 boxes. How may boxes of lettuce should the supermarket purchase for tomorrow? (Assume demand is normally distributed)